System and method for direct imaging

ABSTRACT

A direct imaging system comprises an illumination unit comprising a plurality of light sources, the plurality of light sources configured to emit a plurality of beams, an optical system for forming the plurality of beams to be aligned in position or angle, an acoustic optical modulator positioned to receive the plurality of beams aligned in one of position or angle and to consecutively diffract different portions of the plurality of beams as an acoustic wave propagates in an acoustic direction, and a scanning element adapted to scan an exposure plane with the plurality of beams modulated by the acoustic optical modulator at a scanning velocity, wherein the scanning velocity is selected to incoherently unite the different portions of the plurality of beams into a single exposure spot.

FIELD OF THE INVENTION

The present invention, in some embodiments thereof, relates to DirectImaging (DI) using acoustic modulation and, more particularly, but notexclusively, to direct imaging with semiconductor Laser Diodes (LDs).

BACKGROUND OF THE INVENTION

In Direct Imaging (DI) systems, a scanning beam is used to directlywrite an image, one or more pixels at a time onto an exposure surfacesuch as a photoresist. The image is sometimes obtained by modulating thescanning beam with an Acoustic Optical Modulator (AOM) also called aBragg cell. The AOM uses the acousto-optic effect to diffract anddeflect light using sound waves (usually at radio-frequency) based onstored image data. Once modulated, scanning is typically provided in araster pattern by reflecting the modulated beam off a multi-facetedrotating polygon as the exposure surface (or scanning beam) advances ina scan direction.

In some known systems, the Scophony scanning effect is used to minimizespatial blurring of a generated pattern caused by: a) a finite velocityof the acoustic wave in the modulator and b) a continuous nature of thelaser illuminator. A requirement for the Scophony scanning effect isthat the acoustic velocity of the sound wave in the AOM, increased by amagnification ratio of the optical system between the AOM and exposuresurface, is equal to the scan speed of a writing spot on the exposuresurface, but in the opposite direction. The Scophony scanning effectleads to “standing” data information on a predetermined place on theexposure surface.

U.S. Pat. No. 4,205,348 entitled “Laser scanning utilizing facettracking and acousto pulse imaging techniques,” the contents of which isincorporated herein by reference, describes a method and apparatus forimproving the efficiency and resolution of laser scanning systems usinga multi-faceted rotating polygon as the scanner device. An acousto-opticBragg cell is utilized as an active optical element both modulate anddeflect an incident laser beam so that the modulated beam is caused totrack one facet of the scanner during a complete scan and to shift tothe adjacent facet for the following scan. In order to provide facettracking the acoustic carrier frequency must vary in timesynchronization with the scanning action of the surface of the recordingmedium. It is described that imaging of the input electrical signal onthe recording medium surface is accomplished without blurring, using theScophony scanning effect by moving the image of the acoustic pulses atthe surface of a recording medium at the same relative velocity, in theopposite direction, as the velocity of the laser recording, or writebeam.

U.S. Pat. No. 5,309,178 entitled “Laser marking apparatus including anacoustic modulator,” the contents of which is incorporated herein byreference, describes a laser marking apparatus includes at least onelaser beam source, a multichannel acoustic modulator defining aplurality of at least partially overlapping modulation regions,apparatus for directing at least one laser beam from the at least onelaser beam source through the multichannel acoustic modulator such thateach laser beam extends across at least two of the at least partiallyoverlapping modulation regions, and imaging apparatus for directinglight from the modulator to a laser marking image plane.

The laser beam source is operated in continuous wave mode. It isdescribed that a Laser Diode (LD) is used as the laser beam source forscanning a recording medium with a material of high photosensitivity.Optionally, a pair of LDs, each with a corresponding driver, aretardation plate and a collimation lens is as the laser beam source.When employing the pair of LDs, the retardation plates rotate thepolarization vectors of the LDs so that they can be combined withoutloss of energy by a polarizer beam splitter.

U.S. Pat. No. 6,770,866 entitled “Direct pattern writer,” the contentsof which is incorporated herein by reference, describes an apparatus forscanning a beam across a surface including a scanner scanning a pulsedlaser beam across a surface and a position indicator receiving an inputfrom the pulsed laser beam at a plurality of locations across thesurface, and outputting position indications indicating a position ofsaid pulsed laser beam along said surface. The position indications areused to modulate data in apparatus for exposing patterns on surfaces,for example electrical circuit patterns on photosensitized surfaces. Oneuse of such apparatus is the manufacture of electrical circuits. It isdescribed that edge fixing is accomplished by employing the Scophonyscanning effect.

U.S. Pat. No. 7,046,266 entitled “Scanner System,” the contents of whichis incorporated herein by reference, describes a method of scanning forwriting a pattern on a surface. The method includes providing a scanningbeam comprised of a plurality of independently addressable sub-beams, anunmodulated energy of said scanning beam having a generally Gaussianprofile; scanning the surface with said scanning beam a plurality oftimes, said sub-beams scanning the surface side-by side in thecross-scan direction, each said sub-beam being modulated to reflectinformation to be written; and overlapping the beams in successive scansin the cross-scan direction such that all written areas of the surfaceare written on during at least two scans. Modulation is provided by anacosto-optic modulator (Bragg cell). The Scophony effect is used todecrease or remove blur of generated edges in the scan direction offlying spot scanners.

There is also described a scanning apparatus with a beam comprisingenergy at two distinct spectral lines, modulated by data; and an opticalsystem that receives the beam and focuses it on the surface, such that apattern is written on the surface by the at least one beam and such thatthe energy at both spectral lines is focused on the surface at the sameposition. Focusing at the same position is provided by designing theentrance and exist faces of the AOM such that the difference inrefraction for the two beams (at the different wavelengths) at the inputand output faces is exactly equal and opposite to the difference inBragg angles for the beams. Thus, the two beams which enter together,exit together.

U.S. Patent Publication No. 2007/0058149, entitled “Lighting System andExposure Apparatus,” the contents of which is incorporated herein byreference, describes a method and apparatus for illuminating a recordingmedium with two dimensional array of semiconductor LDs. The twodimensional array of LDs are used to replace lower efficiency mercurylamps or excimer lasers. Diffused beams output from the two-dimensionalarray of LDs are converted into high-directivity beams with spreadangles equalized circumferentially by two kinds of cylindrical lenses.Tilt in optical axis of individual beams due to misalignment with thecenter of the beam is corrected by a two dimensional array wedged glass.The beams are modulated with a two-dimensional light modulator such as amask or a Digital Mirror Device (DMD) for maskless exposure.

SUMMARY OF THE INVENTION

According to an aspect of some embodiments of the present inventionthere is provided a system and method for Direct Imaging (DI) with oneor more arrays of light sources modulated with an Acoustic OpticalModulator (AOM). According to some embodiments of the present invention,the system and method for DI combines beams from the one or more arraysof light sources incoherently toward a single exposure spot using theScophony principle. Optionally, the one or more arrays of beam sourcesare an array of low power beam sources, e.g. LDs. Optionally, beams fromdifferent arrays are combined for scaling power of the beams.Optionally, the array of light sources is an array of light sourcesincluding multiple wavelengths.

According to an aspect of some embodiments of the present inventionthere is provided a direct imaging system comprising an illuminationunit comprising a plurality of light sources, the plurality of lightsources configured to emit a plurality of beams, an optical system forforming the plurality of beams to be aligned in position or angle, anacoustic optical modulator positioned to receive the plurality of beamsaligned in one of position or angle and to consecutively diffractdifferent portions of the plurality of beams as an acoustic wavepropagates in an acoustic direction, and a scanning element adapted toscan an exposure plane with the plurality of beams modulated by theacoustic optical modulator at a scanning velocity, wherein the scanningvelocity is selected to incoherently unite the different portions of theplurality of beams into a single exposure spot.

Optionally, the plurality of light sources is plurality of semiconductorlaser diodes.

Optionally, at least one light source of the plurality of light sourcesis adapted to emit light at a different wavelength than at least oneother light source of the plurality of light sources.

Optionally, the plurality of light sources emits light at a rangebetween 370-410 nm.

Optionally, at least one light source of the plurality of light sourcesis adapted to have a polarization that is different than at least oneother at least one light source of the plurality of light sources.

Optionally, the plurality of light sources is arranged in one or morearrays, wherein each array aligned with a scan direction of the directimaging system.

Optionally, each of the arrays includes 2-100 light sources.

Optionally, only a portion of the light sources are operated at a time.

Optionally, the scanning element is a rotating polygon including aplurality of facets, and wherein portion of the light sources that areoperated are selected responsive to an angle of one of the plurality offacets during scanning.

Optionally, each light source in the plurality of light sources isassociated with a dedicated lens, wherein the dedicated lens is adaptedto shape a beam emitted from a light source.

Optionally, the dedicated lens is adapted to shape the beam to beelongated in a direction perpendicular to the scan direction.

Optionally, the dedicated lens is adapted to shape the beam to beelongated in a direction perpendicular to the cross-scan direction.

Optionally, the acoustic optical modulator is associated with anaperture for receiving the plurality of beams and wherein the dedicatedlens and the optical system is adapted to shape the beam to fill theaperture in at least one of a direction perpendicular to a scandirection and a direction perpendicular to a cross-scan direction.

Optionally, the optical system includes an element adapted to collimatebeams from the plurality of light sources directed toward the acousticoptical modulator.

Optionally, the optical system includes a telecentric optical systemadapted to direct the plurality of beams to an aperture of the acousticoptical modulator.

Optionally, each of the different portions of the plurality of beamsincludes a portion from each of the plurality of beams received from theacoustic optical modulator.

Optionally, each of the different portions of the plurality of beamsincludes one or more beams from the plurality of beams.

Optionally, the scanning velocity is defined to match an acousticvelocity of acoustic optical modulator times a magnification ratio ofthe system but in an opposite direction.

Optionally, the acoustic optical modulator is a multi-channel acousticoptical modulator.

Optionally, the system addition comprises at least two of theillumination unit and at least one optical element for combiningcorresponding beams from the at least two of the illumination unit.

Optionally, corresponding beams from the more than one illumination unitdiffer in at least one of wavelength and polarization.

According to an aspect of some embodiments of the present inventionthere is provided a method for direct imaging, the method comprisingproviding an illumination unit including a plurality of light sourcesadapted to emit a plurality of beams, directing the plurality of beamstoward an acoustic optical modulator so that the plurality of beams arealigned one of position or angle, consecutively diffracting differentportions of the plurality of beams while an acoustic wave propagates inan acoustic direction, and scanning an exposure plane in a scandirection with output from the acoustic optical modulator, wherein thescanning is performed at a scanning velocity, and wherein the scanningvelocity is selected to incoherently unite the different portions of theplurality of beams into a single exposure spot.

Optionally, the plurality of light sources includes is a plurality ofsemiconductor laser diodes.

Optionally, at least one light source of the plurality of light sourcesis adapted to emit light at a different wavelength than at least oneother light source in the plurality of light sources.

Optionally, the array of light sources emits light at a range between370-410 nm.

Optionally, at least one light source of the plurality of light sourcesis adapted to have a polarization that is different than at least oneother light source in the plurality of light sources.

Optionally, the plurality of light sources is arranged in one or morearrays, wherein each array aligned with a direction of the scanning.

Optionally, each of the arrays includes 2-100 light sources. Optionally,the method further comprises operating only a portion of the lightsources at a time.

Optionally, the portion of the light sources that are operated areselected responsive to an angle of a facet used for the scanning.

Optionally, the method further comprises shaping each of the pluralityof beams to be elongated in a direction perpendicular to a scandirection of the scanning.

Optionally, the method further comprises shaping each of the pluralityof beams to be elongated in a direction perpendicular to a cross-scandirection of the scanning.

Optionally, the method further comprises shaping each of the pluralityof beams to fill an aperture of the acoustic optical modulator in atleast one of a direction perpendicular to a scan direction of thescanning and a direction perpendicular to a cross-scan direction of thescanning.

Optionally, each of the different portions of the plurality of beamsincludes a portion from each of the plurality of beams received from theacoustic optical modulator.

Optionally, each of the different portions of the plurality of beamsincludes one or more beams from the plurality of beams.

Optionally, the method further comprises collimating beams from theplurality of light sources directed toward the acoustic opticalmodulator.

Optionally, the method further comprises matching an acoustic velocityof acoustic optical modulator times a magnification ratio of the systembut in an opposite direction.

Optionally, the method further comprises providing a plurality ofillumination units and combining corresponding beams from the pluralityof illumination units.

Optionally, the corresponding beams from the more plurality ofillumination units differ in at least one of wavelength andpolarization.

According to an aspect of some embodiments of the present inventionthere is provided a method for facet tracking in a direct imagingsystem, the method comprising providing an array of light sourcesadapted to emit an array of beams, wherein the array of light sources isaligned with a scan direction of the direct imaging system, directingthe beams from the array of lights sources toward an acoustic opticalmodulator so that the plurality of light sources project light along alength greater than length of a single facet of a rotating polygon usedfor scanning, scanning an exposure plane in the scan direction withoutput from the acoustic optical modulator, and selectively operatingdifferent subsets of the lights sources in coordination with rotation ofthe polygon, wherein the subsets of the light sources selected are lightsources that impinge on a facet used for scanning.

Optionally, the method further comprises adjusting each light source ofarray to have a different angle of incidence in acoustic opticalmodulator so that the plurality of beams operated impinge along a lengthof the facet used for scanning.

Optionally, the method further comprises turning off light sources fromthe plurality of light sources that emit beams that impinge near or pastan edge of the facet used for scanning in coordination with rotation ofthe polygon.

Optionally, the method further comprises incoherently uniting theplurality of beams operated into a single exposure spot.

Unless otherwise defined, all technical and/or scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which the invention pertains. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of embodiments of the invention, exemplarymethods and/or materials are described below. In case of conflict, thepatent specification, including definitions, will control. In addition,the materials, methods, and examples are illustrative only and are notintended to be necessarily limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments of the invention are herein described, by way ofexample only, with reference to the accompanying drawings. With specificreference now to the drawings in detail, it is stressed that theparticulars shown are by way of example and for purposes of illustrativediscussion of embodiments of the invention. In this regard, thedescription taken with the drawings makes apparent to those skilled inthe art how embodiments of the invention may be practiced.

In the drawings:

FIG. 1 is a simplified block diagram of an exemplary DI scanning systemin accordance with some embodiments of the present invention;

FIG. 2 is a simplified schematic drawing of an exemplary array of lightsources in accordance with some embodiments of the present invention;

FIG. 3A is a schematic diagram of an exemplary optical design forarranging individual beams of the array inside an aperture of an AOM inaccordance with some embodiments of the present invention;

FIG. 3B is a schematic diagram of an exemplary optical design forshaping an individual beam in a scan and cross-scan direction inaccordance with some embodiments of the present invention;

FIG. 3C showing a simplified schematic diagram of beams imaged on an AOMand a pupil plane in accordance with some embodiments of the presentinvention;

FIG. 4A is a schematic diagram of an alternate exemplary optical designfor arranging individual beams of the array inside an aperture of an AOMin accordance with some embodiments of the present invention;

FIG. 4B is a schematic diagram of an alternate exemplary optical designfor shaping an individual beam in a scan and cross-scan direction inaccordance with some embodiments of the present invention;

FIG. 4C showing a simplified schematic diagram of beams imaged on an AOMand a pupil plane in an alternate exemplary optical design in accordancewith some embodiments of the present invention;

FIG. 5 is an exemplary optical path of a beam forming optical system ina DI system in accordance with some embodiments of the presentinvention;

FIG. 6 is a schematic diagram showing an exemplary array of light beamsarranged in a multi-channel AOM in accordance with some embodiments ofthe present invention;

FIG. 7 is an exemplary schematic illustration of light beam modulationusing the Scophony scanning effect over three different time frames inaccordance with some embodiments of the present invention;

FIG. 8 is a simplified schematic drawing of an exemplary matrix of lightsources formed into a writing beam in accordance with some embodimentsof the present invention;

FIG. 9A, 9B, 9C and 9D are exemplary schematic diagrams of a matrix ofbeams arranged in a plurality of arrays as imaged on AOM planes andcorresponding pupil planes in accordance with some embodiments of thepresent invention;

FIGS. 10A, 10B, 10C and 10D are simplified schematic drawingsillustrating a facet tracking method in accordance with some embodimentsof the present invention;

FIG. 11 is a simplified schematic drawing of a exemplary illuminationunit including two arrays of light sources and optics for combiningbeams from the two arrays in accordance with some embodiments of thepresent invention;

FIG. 12 is a schematic diagram of an exemplary optical design forcombining beam from different arrays in accordance with some embodimentsof the present invention; and

FIG. 13 is an exemplary DI system in accordance with some embodiments ofthe present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

The present invention, in some embodiments thereof, relates to DI usingacoustic modulation and, more particularly, but not exclusively, todirect imaging with semiconductor LDs.

According to some embodiments of the present invention there is provideda DI system that uses one or more arrays of light sources modulated byan AOM to form a writing beam for scanning a recording medium. In someexemplary embodiments, the array of light sources is a dense array, e.g.including 50 light sources or 2-100 light sources, that is shaped toform the writing beam. In some exemplary embodiments, a plurality ofarrays and/or matrix of light sources including 50×10 light sources isused to form a writing beam. Optionally, the array includes lightsources with different spectral properties, for example, light sourceswith different wavelengths, e.g. ranging between 370-410 nm and/ordifferent polarizations. Typically, the light sources in the array areoperated in continuous wave mode. In some exemplary embodiments, thearray is an array of semiconductor LDs.

Typically, the system includes a scanning optical system for imaging theplane of the AOM onto a recording medium, e.g. panel to be exposed at adesired magnification. According to some embodiments of the presentinvention, the scanning optical system is achromatic over the wavelengthrange of the array of light sources. Typically, a polygon mirrordeflects the beam to provide raster scanning.

According to some embodiments of the present invention, a DI methodprovides for repeatedly exposing spots on the recording medium withdifferent light sources in the array(s) during a single scanning sweepof the DI system. According to some embodiments of the presentinvention, the repetitive exposure over a single sweep is provided byapplying the Scophony scanning effect.

According to some embodiments of the present invention, the lightsources in each of the one or more arrays are arranged laterally in theAOM along the acoustic direction so that as the acoustic wavepropagates, the wave consecutively switches individual beams in each ofthe one or more arrays. In some exemplary embodiments, the beams areshaped to span an acoustic direction of the AOM so that as the acousticwave propagates, the acoustic wave consecutively switches portions ofall the beams in the one or more arrays. According to some embodimentsof the present invention, the Scophony scanning effect is used tocoordinate the velocity of the acoustic wave and the magnificationprovided by a scanning optical system with the scanning velocity so thateach of the switched beams in the array impinge the recording medium ina same spot.

In some exemplary embodiments, the AOM is a multi-channel AOM, e.g. a 24channel AOM or 4-1000 channel AOM and multiple pixels (or spots) arewritten simultaneously during scanning, each of which can berepetitively exposed over a single sweep by applying the Scophonyscanning effect as described herein. In some exemplary embodiments,beams from individual light sources in the one or more arrays are shapedto be elongated in the cross-scan direction and the channels of themulti-channel AOM are arranged along the cross-scan directions so thateach channel modulates a different portion of each elongated beams. Inother exemplary embodiments, each of the beams from individual lightsources in the array is shaped to fill an entire area of an aperture ofthe AOM.

The present inventors have found that repetitive exposure with aplurality of semiconductor LDs using the Scophony scanning effect asdescribed herein may provide a plurality of advantages. Optionally, someof the advantages are associated with reducing a bill of material of aDI system by replacing the laser units typically used for DI with alower cost array of light sources, e.g. semiconductor LDs, each of whichoperate at a lower power, e.g. 5-50 W laser light source or 0.1-2 Wsemiconductor LD. Specifically, semiconductor LDs as compared to pulsedsolid-state lasers of previous systems are lower in cost, are relativelyservice free and have a relatively longer lifetime. In some exemplaryembodiments, repeated exposure with low power light sources using the DIsystem and method described herein provides for scanning material of lowphotosensitivity. The present inventors have found that, repeatedexposure of a same spot with a plurality of lower power LDs provides theaccumulated energy required to write on a material having lowphotosensitivity. In some exemplary embodiments, repeated exposure witha plurality of light sources allows for using light sources with highertolerances typically associated with lower cost light sources since theresulting spatial profile and spectrum can be defined by the averageproperties of the light sources. The present inventors have also foundthat the repetitive exposure with a plurality of light sources providesa smoothing effect that improves the overall quality of the exposure. Insome exemplary embodiments, the array of light sources includes one ormore auxiliary light sources that can be operated when another lightsource in the array malfunctions. The present inventors have found thatby including auxiliary light sources in the array, lower cost lightsources typically associated with lower reliability can be used withoutcompromising lifetime and/or reliability of the light source unit.Optionally, the redundancy provided by the auxiliary light sourcesallows the illumination unit to continue operating even if some lightsources fail. Optionally, the plurality of light sources is combined toshape a desired spectrum. Another advantage of LDs is its relativelyhigh wall-plug efficiency, e.g. as compared to known gas lasers andknown Dioded-Pumped Solid State (DPSS) lasers.

According to some embodiments of the present invention, the DI systemand methods described herein provide improved versatility over known DIsystems. In some exemplary embodiments, the array of light sourcesincludes light sources with different spectral characteristics.Optionally, the array includes light sources having differentwavelengths. Typically, shorter wavelengths are used to provide rigidityon a surface of the recording medium while longer wavelengths are usedto penetrate through the recording medium. In some exemplaryembodiments, different wavelengths are used to expose a same spot on theexposure panel. Optionally, for a particular application and/or aparticular sweep, specific light sources (and wavelengths required) inthe array are selected and only those light sources are operated.Optionally, more than one array of light sources is used to scale theoutput power that the illumination unit can provide. Optionally, beamsfrom light sources in the different arrays are combined to form a singlebeam.

According to some embodiments of the present invention, facet trackingis provided by using only a portion of the light sources to write eachpixel or spot on an exposure surface and altering the portion of thelight sources used in synchronization with an orientation of the activefacet used for scanning. During facet tracking, each of the beams or atleast a portion of the beams are formed to impinge the polygon at adifferent position.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not necessarily limited in itsapplication to the details of construction and the arrangement of thecomponents and/or methods set forth in the following description and/orillustrated in the drawings. The invention is capable of otherembodiments or of being practiced or carried out in various ways.

Referring now to the drawings, FIG. 1 illustrates a simplified blockdiagram of an exemplary DI scanning system in accordance with someembodiments of the present invention. According to some embodiments ofthe present invention, an illumination unit 100 includes an array 50 oflight sources 50 ₁, 50 ₂, . . . 50 _(N) providing a plurality of beams65 that are shaped with a beam forming optical system 60 to fit into anaperture 71 of an AOM 70. Typically the light sources are LDs. Accordingto some embodiments of the present invention, the plurality of beams 65are arranged laterally along an acoustic direction of AOM 70 throughaperture 71 and are collimated into a one dimensional array.Alternatively, each of the plurality of beams 65 has a large beamdiameter, e.g. spanning the size of aperture 71 and the beams overlap inone position in the AOM. Typically, AOM 70 modulates incoming beams 65based on image data received from a data control unit 700 and a scanningoptical system 90 images the plane of the AOM including the modulateddata onto exposure plane 95 as beams are deflected from rotating polygon80.

According to some embodiments of the present invention, AOM 70 has anaperture 71, e.g. a large aperture that is optionally rectangular inshape and wide enough (along the acoustic direction 75) to receive thecollimated array of beams 65. Optionally, aperture 71 has a widthbetween 10-40 mm. In some exemplary embodiments, AOM 70 is amultichannel AOM and aperture 71 is wide enough along a directionperpendicular to the acoustic direction 75 to span all channels in AOM70. Optionally, AOM 70 includes between 24-48 channels. In someexemplary embodiments, AOM 70 is formed from an acousto-optical materialthat shows a low acoustic curvature factor. Optionally, AOM 70 is formedfrom a quartz crystal. Optionally AOM is formed from a TeO₂ crystal.

According to some embodiments of the present invention, array 50 is aone dimensional array of LDs. Optionally, the array is a dense array oflight sources that are arranged in a crescent shape so that illuminationfrom a large number of light sources can be directed toward beam formingoptical system 60. In some exemplary embodiments, each LD in the arrayis associated with a dedicated lens 55 _(n) (n=1, 2, . . . N) from alens array 55 that focuses and aligns beams 65 from LDs 55 onto beamforming optical system 60. Typically, lens array 55 is included inillumination unit 100 and is housed in a common housing.

According to some embodiments of the present invention, array 50includes LDs with different wavelengths, optionally ranging between370-410 nm. Optionally, array 50 includes two or more LDs with a samewavelength. In some exemplary embodiments, array 50 includes LDs with apolarization oriented either parallel or perpendicular to the scandirection. In some exemplary embodiments, the LDs are operated incontinuous mode. Typically, light source unit includes between 2 and 100LDs, e.g. 50 LDs. In some exemplary embodiments, array 50 includes acertain amount of redundancy and only portion of the LDs in array 50 areoperated at one time.

According to some embodiments of the present invention, beam formingoptical system is used to shape the individual beams and to arrange theindividual LDs beams inside aperture 71 of AOM 70. In some exemplaryembodiments, beam forming optical system 60 includes single couplingoptics for collimating beams in one plane along an acoustic direction 75of the AOM 70.

In some exemplary embodiments, polygon 80 is similar to the polygondescribed in incorporated U.S. Pat. No. 6,770,866 and includes beamfacet tracking capability for example as described in incorporated U.S.Pat. No. 4,205,348. Optionally facet tracking is achieved by operatingonly a subset of the array during each exposure and consecutivelyshifting the subset operated as the facet rotates as will be describedin more detail herein below. In some exemplary embodiments, polygon 80is rotated at a speed of between 1000-4000 RPM, e.g. 3000 RPM duringoperation. According to some embodiments of the present invention, thescanning optical system 90 is achromatic over the wavelength range ofthe LDs.

According to some embodiments of the present invention and as will bedescribed in more detail herein below, as an acoustic wave propagates inacoustic direction 75, the wave consecutively switches each of beams 65in turn by diffracting them toward polygon 80 for imaging onto exposureplane 95. Optionally, an acoustic wave diffracts more than one of beams65 at a time as it propagates in acoustic direction 75. Typically,undiffracted beams are directed towards an optical stop 10.Alternatively, the opposite may be the case and the undiffracted lightfrom AOM 70 may be imaged onto the recording medium while the diffractedlight may encounter a stop.

Reference is now made to FIG. 2 showing a simplified schematic drawingof an exemplary array of light sources in accordance with someembodiments of the present invention. According to some embodiments ofthe present invention, an illumination unit 100 includes a dense arrayof light sources 50 ₁, 50 ₂, . . . 50 _(N) mounted on a platform 57.Optionally, the array includes between 2 and 100 LDs, e.g. 50 LDs.Typically, illumination unit 100 includes a dedicated lens 55 for eachLD mounted on platform 57 for focusing and aligning each of the beams.Optionally, the LDs are mounted in platform 57 in a crescent shape.Optionally, more than one array, e.g. two arrays of light sources isused.

Reference is now to FIG. 3A showing a schematic diagram of an exemplaryoptical design for arranging individual beams of the array inside anaperture of an AOM in accordance with some embodiments of the presentinvention. According to some embodiments of the present invention, thebeam forming optical system includes a cylindrical lens 11 forcollimating beams 65 from the individual LDs in the crescent shapedarray 50 along an acoustic direction 75. Typically, the acousticdirection 75 is parallel to the scan direction. According to someembodiments of the present invention, the optical design additionallyincludes a telecentric telescope lens system 62 to relay beams along anacoustic direction 75 into aperture 71 of AOM 70 and all the beams areincident in the AOM at their Bragg angle. Typically, telecentrictelescope lens functions to size the beams so that they fit intoaperture 71 and enter aperture 71 as an array of parallel beams.Optionally variable beam expansion for the cross-scan direction isprovided by adjusting distances between beam adjustment lenses 63.According to some embodiments of the present invention, a cylindricallens 83 bends individual beams diffracted from AOM so that the beamsimpinge a pupil plane at same spot but from different angles. Accordingto some embodiments of the present invention and as will be described inmore detail herein below, the individual beams are diffractedconsecutively with the AOM as an acoustic wave propagates in acousticdirection 75 but are exposed on a same spot on an exposure plane byusing the Scophony principle.

Reference is now made to FIG. 3B showing a schematic diagram of anexemplary optical design for shaping an individual beam in the scandirection and cross-scan direction respectively and to FIG. 3C showing asimplified schematic diagram of beams imaged on an AOM and a pupil planeboth in accordance with some embodiments of the present invention. Asshown, a solid line 651 _(n) represent a ray of individual beam 65 _(n)in a fast axis aligned with the scan direction 85 and a dashed line 652_(n) represents a ray of beam 65 in a slow axis typically aligned withthe cross scan direction 86. According to some embodiments of thepresent invention, in an AOM plane and/or object plane 73, e.g. exposureplane, each LD beam, 65 ₁, 65 ₂, 65 ₃, . . . 65 n, . . . 65 _(N) isformed to have a narrow beam waist along scan direction 85 and is formedto be elongated along cross-scan direction 86. Optionally, the beam hasa near Gaussian beam profile, e.g. M²˜1.5 along a fast axis and a higherorder beam profile, e.g. M²˜7 along slow axis of the beam. In someexemplary embodiments, collimating lens 61 adjusts the beam waist to adesirable width in the scan direction. Typically, the beams in theexposure plane are an image of the beams in the AOM plane while thepupil plane is a conjugated plane to both the AOM plane and exposureplane.

According to some embodiments of the present invention, in a pupil plane89 (FIG. 3C), all beams 65 ₁, 65 ₂, 65 ₃, . . . 65 _(N) from LDs 50 ₁,50 ₂, 50 ₃, . . . 50 _(N) impinge at same spot but from differentangles. According to some embodiments of the present invention, each ofbeams 65 ₁, 65 ₂, 65 ₃, . . . 65 _(N) are formed to have a wide beamwaist along the scan direction 85 (in scan pupil plane 87) and is formedto have a narrow beam waist along a cross-scan direction 86 (incross-scan pupil plane 84). Typically, pupil plane 89 (FIG. 3C) is avirtual plane composed from physical scan pupil plane 87 typicallycoinciding with a facet plane of polygon 80 and cross-scan pupil planetypically positioned between AOM 70 and a facet plane of polygon 80(FIG. 3B).

Reference is now to FIG. 4A showing a schematic diagram of an alternateexemplary optical design for arranging individual beams of the arrayinside an aperture of an AOM in accordance with some embodiments of thepresent invention. According to some alternate embodiments of thepresent invention, the beam forming optical system shapes the beams tohave a large beam diameter both in the scan and cross-scan direction.Typically, each of beams in beam array 65 is shaped to fill aperture 71.Typically, a cylindrical lens 61 collimates beams from individual LDs inthe array 50 along an acoustic direction 75 and a lens system 72 relaysthe beams into aperture 71 of AOM 70 so that the individual beamsoverlap in one position in AOM 70. Although, the individual beamsoverlap, each of the beams impinge the AOM crystal at different angles,e.g. slightly different angles but typically close to the Bragg angle.

According to these alternate embodiments of the present invention,individual beams diffracted from AOM impinge a pupil plane at differentspots but from the same angle and impinge exposure plane 95 (FIG. 1) ata same spot but from different angles. In these embodiments, a portionof all the large diameter beams, e.g. the active beams are diffractedsimultaneously. As will be described in more detail herein below,subsequent portions of all the large diameter beams are diffracted in aconsecutive manner as an acoustic wave propagates in acoustic direction75 but are exposed on a same spot on an exposure plane by using theScophony principle.

Reference is now made to FIG. 4B showing a schematic diagram of analternate exemplary optical design for shaping an individual beam in thescan direction and cross-scan direction respectively and to FIG. 4Cshowing a simplified schematic diagram of beams imaged on an AOM and apupil plane in an alternate exemplary optical design both in accordancewith some embodiments of the present invention. As shown, a solid line651 _(n) represent a ray of individual beam 65 _(n) in a fast axisaligned with scan direction 85 and dashed line 652 _(n) represents a rayof beam 65 _(n) in a slow axis typically aligned with the cross-scandirection 86. According to some embodiments of the present invention, inAOM and/or object plane 73, each LD beam, 65 ₁, 65 ₂, 65 ₃, . . . 65_(n), . . . 65 _(N) is formed to have a large beam waist both in scandirection 85 and cross-scan direction 86 that fill aperture 71 in boththe scan and cross-scan direction. Optionally, the beam has a nearGaussian beam profile, e.g. M²˜1.5 along a fast axis and a higher orderbeam profile, e.g. M²˜7 along slow axis of the beam. In some exemplaryembodiments, collimating lens 61 adjusts the beam waist to a desirablewidth in the scan direction. Optionally variable beam expansion isprovided in cross-scan direction by adjusting distances between beamadjustment lenses (not shown for simplicity).

According to some embodiments of the present invention, in a pupil plane89, all beams 65 ₁, 65 ₂, 65 ₃, . . . 65 _(N) from LDs 50 ₁, 50 ₂, 50 ₃,. . . 50 _(N) impinge at different spots but from a same angle.According to some embodiments of the present invention, each of beams 65₁, 65 ₂, 65 ₃, . . . 65 _(N) are formed to have a narrow beam waistalong both scan direction 85 (in scan pupil plane 87) and cross-scandirection 86 (in cross-scan pupil plane 84). Typically, pupil plane 89(FIG. 4C) is a virtual plane composed from physical scan pupil plane 87typically coinciding with a facet plane of polygon 80 and cross-scanpupil plane typically positioned between AOM 70 and a facet plane ofpolygon 80 (FIG. 4B).

Reference is now made to FIG. 5 showing an exemplary optical path of abeam forming optical system in the DI system in accordance with someembodiments of the present invention. According to some embodiments ofthe present invention, illumination from a dense array of LDs 50 iscollimated with a collimating lens 61 and directed via a plurality ofreflecting surfaces 66 toward AOM 70 for beam modulation. Typically eachof the LDs in the array is associated with a dedicated lens, e.g. fromlens array 55 for focusing the beams onto collimating lens 61.Optionally, LDs in the array include LDs of different wavelengths and/orpolarizations. In some exemplary embodiments, only a portion of the LDsin array 50 are operated during scanning. In some exemplary embodiments,each of the beams from the array is shaped in the cross-scan directionwith lens 63 and is relayed onto the AOM with a pair of telescope lenses62. Optionally, beam expansion in the cross-scan direction is adjustableby adjusting distance between lenses 63.

Reference is now FIG. 6 showing a schematic diagram of an exemplaryarray of light beams arranged in a multi-channel AOM in accordance withsome embodiments of the present invention. According to some embodimentsof the present invention, an array of illumination beams 65 that arecollimated are arranged along scan direction 85 and/or acousticdirection 75 enter an aperture 71 of AOM 70. Optionally, 2-100illumination beams are arranged along acoustic direction 75. Typically,each beam 65 is shaped to be elongated along a direction perpendicularto acoustic direction. Typically each beam is modulated over a pluralityof acoustic channels with electrode array 79. Typically, electrode array79 is arranged along an axis perpendicular to acoustic direction 75optionally aligned with cross-scan direction 86. Typically, the multiplechannels provide for writing more than one pixel at a time.

During operation, RF signals are transmitted to electrodes 79 based on amodulation pattern initiating acoustic sound waves to propagate inacoustic direction 75 from a position of electrodes 79. According tosome embodiments of the present invention, when an acoustic wavepropagates along an acoustic channel, the wave consecutively diffractsthe portion of each of beams of array 65 associated with the triggeredacoustic channel. According to some embodiments of the presentinvention, since all beams in a same channel are modulated by a samesignal, all the beams in the channel are modulated in a same manner. Insome exemplary embodiments, an acoustic wave packet modulates aplurality of beams from array 65 at a time.

Reference is now made to FIG. 7 showing an exemplary schematicillustration of an image of an AOM window over three different timeframes of acoustic wave packet propagation in accordance with someembodiments of the present invention (denoted by t₁, t₂, t₃). Typically,an image 88 of AOM 70 is moved across exposure plane 95 with a velocity,vscan in scan direction 85 with rotating polygon 80 (FIG. 1). Although,the entire image is moved in scan direction 85, only a portion 110 ofimage 88 that coincides with a position of the acoustic wave packet isdiffracted toward exposure panel 95. That portion 110 of image 88 thatcoincides with a position on the acoustic wave packet moves in acousticdirection 75 (opposite scan direction 85) at a velocity determined bythe velocity of the acoustic wave packet and the magnification ofscanning optical system 90.

According to some embodiments of the present invention, the scanningvelocity, vscan, is adjusted to be equal in magnitude but opposite indirection to acoustic velocity, vacoust (vscan=−vacoust), so that anadvancing acoustic wave packet in moving AOM window 88 always diffractsa portion 110 of image 88 toward a same spot 951 on exposure panel 95.Therefore, spot 951 is stationary in an exposure plane of the recordingmedium and can be consecutively illuminated by all individual laserdiode beams. In this manner the beams are combined incoherently.Optionally scan lines are overlapped in the cross-scan direction forsmooth energy profile.

Reference is now made to FIG. 8 showing simplified schematic drawing ofan exemplary matrix of light sources formed into a writing beam inaccordance with some embodiments of the present invention. According tosome embodiments of the present invention, an illumination unit 101includes a matrix 555 of light sources 50 ₁₁, 50 ₁₂, . . . 50 ₂₁, 50 ₂₂,. . . 50 _(NM) and/or more than one array of light sources providing aplurality of beams 665 that are shaped with dedicated lens, e.g. similarto lenses 55 (FIG. 1) and beam forming optical system 666 to fit into anaperture 71 of an AOM 70. According to some embodiments of the presentinvention, the matrix 555 is arrange on a concave shaped plane so thatillumination from a large number of light sources can be directed towardbeam forming optical system 666. In some exemplary embodiments, each LDin matrix 555 is associated with a dedicated lens (not shown forsimplicity sake) that focuses and aligns beams 665 from LDs 555 ontobeam forming optical system 666. According to some embodiments of thepresent invention matrix 555 includes 1-20 arrays of 2-100 lightsources.

According to some embodiments of the present invention, the number ofbeams 665 that can be coupled into the system is limited by an angularacceptance range of scan optics 90 and a size of aperture 71. Typically,the angular acceptance range is different for scan direction 85 andcross-scan direction 86 and is determined by a numerical aperture ofscan optics 90 in image plane 95 and the magnification of the systembetween AOM 70 and image plane 95. According to some embodiments of thepresent invention, for a given angular acceptance range, a size of abeam in aperture 71 of AOM 70 from a single LD can be calculated, e.g. asmallest achievable beam size can be calculated. Typically, the smallestachievable beam depends on the beam parameter product (M²) of the LDwhich is a measure an angular divergence of the beam for a given spotsize. According to some embodiments of the present invention, once asize of a single beam in aperture 71 is calculated, the size of aperture71 defines a number of LD beams that fit into aperture 71 each of whichhas an angular divergence that fits into the angular acceptance range ofscan optics 90. Typically, the number of rows versus columns in matrix555 depends both on dimensions of aperture 71. Typically, AOM 70modulates incoming 665 based on image data received from a data controlunit 700 and a scanning optical system 90 images the plane of the AOMincluding the modulated data onto exposure plane 95 as beams aredeflected from rotating polygon 80.

Reference is now made to FIGS. 9A, 9B, 9C and 9D showing exemplaryschematic diagrams of beams arranged in a plurality of arrays as imagedon AOM planes and corresponding pupil planes in accordance with someembodiments of the present invention. For exemplary purposes, beamforming of beams from a matrix 555 including only 5 LDs along cross-scandirection 86 and 12 LDs along scan direction 85 is shown. Typically, theaperture in pupil plane is an angular aperture. Typically, a matrix 555of an illumination unit 101 includes 50×10 LDs that are formed withoptical system 666 to fit into aperture 71. According to someembodiments of the present invention, beams in matrix 555 can be formedin a plurality of different configurations to form a writing beam.

Referring now to FIG. 9A, in some exemplary embodiments, beams 665 areformed to be narrow both in a cross-scan and scan direction and arearranged in a staggered matrix formation in AOM plane to form image 701.In some exemplary embodiments, in image 701, each of beams 665 impingeAOM plane 733 from a same angle but in a different position. In theseembodiments, each beam in corresponding pupil plane 899 impinges at asame position and fills an entire aperture.

Referring now to FIG. 9B, in some exemplary embodiments, beams 665 areformed to be wide in cross-scan direction 86 and narrow in scandirection 85 and are arranged in a staggered column array in AOM planeto form image 702. According to some embodiments of the presentinvention, beams 665 from each of the different rows in each column,e.g. the five rows are formed to impinge AOM plane 733 at a sameposition but from different angles while beams 665 from each of thedifferent columns are formed to impinge AOM plane 733 at a differentposition but at a same angle. In these embodiments, the resulting image702 in AOM plane 733 is typically a single array including a number ofwide spots corresponding to the number of columns, e.g. 12 columns thatare staggered along scan direction 85. According to some embodiments ofthe present invention, in corresponding pupil plane 899, the resultantimage 802 is an image 802 including a single array of wide spotsstaggered along cross-direction corresponding to the number of rows,e.g. 5 rows. Typically in these embodiments, in the pupil plane 899,beams 655 from the different columns but from a same row impinge in asame spot.

Referring now to FIG. 9C, in some exemplary embodiments, beams 665 areformed to be wide in scan direction 85 and narrow in cross-scandirection 86 to form image 703. In these embodiments, beams 665 fromeach of the different columns in each row, e.g. 12 columns are formed toimpinge AOM plane 733 at a same position but from different angles whilebeams 665 from each of the different rows are formed to impinge AOMplane 733 at a different position but at a same angle. Typically, theresultant image 703 in AOM plane 733 is a single array including anumber of wide spots corresponding to the number of rows, e.g. 5 rowsthat are staggered along cross-scan direction 86. In these embodiments,in corresponding pupil plane 899, beams 655 form image 803 of a singlearray including a number of wide spots corresponding to the number ofcolumns, e.g. 12 columns that are staggered along scan direction 85. Inimage 803 of pupil plane 899, beams 655 from different rows but from asame column typically impinge in a same spot.

Referring now to FIG. 9D, in some exemplary embodiments, beams 665 areformed with optical system 666 to impinge at a same position and fillaperture 71 in both scan direction 85 and cross-scan direction 86, eachfrom a different angle to form image 704. According to some embodimentsof the present invention, in corresponding pupil plane 899, each ofbeams 665 impinge at a different position and from a matrix formation inboth a scan and cross-scan direction (is formed) in image 804. In theseembodiments, each of beams 665 in pupil plane 899 is typically narrow inboth scan direction 85 and cross-scan direction 86.

According to some embodiments of the present invention, beams 665 areformed so that an average cross-scan beam profile in aperture 71 issmooth since consecutive scan lines are overlapped in the cross-scandirection. Typically, image 702 provides a smoother profile incross-scan direction as compared to image 703. Optionally, the staggeredmatrix formation of beams 655 in image 701 provides overlapping incross-scan direction 86 which can improve the smoothness of the profile.

Reference is now made to FIGS. 10A-10D showing simplified schematicdrawings that illustrate a facet tracking method in accordance with someembodiments of the present invention. According to some embodiments ofthe present invention, facet tracking is achieved by sequentiallyturning ON and OFF different LDs in array 50 in coordination withrotation of polygon 80 and/or angle of facet of polygon 80, used forscanning, e.g. facet 81.

According to some embodiments of the present invention, light sources 50are arranged and/or their respective beams are formed such that eachlight source from array 50 projects a beam that impinges facet 81 at adifferent position along a length L of facet 81. Optionally,distribution of the impinging beams along the length of facet 81 isachieved by adjusting each light source of array to have a differentangle of incidence in AOM 70. Optionally, the desired distribution alongthe length of facet 81 is achieved with a cylindrical lens 83. In someexemplary embodiments, beams from light sources in array 50 are arrangedand/or formed to project light along a length greater than length L of asingle facet.

According to some embodiments of the present invention, as polygon 80rotates, a different set of light sources provides beams that impinge onfacet 81, while the other light sources that emit beams that impingenear or past an edge of facet 81 are turned off and/or not used towriting. Typically, for each spot or pixel written, a different set oflight sources is used. Alternately, the set of light sources used isaltered for every other spot or pixel written and/or after a pluralityof spots are written.

By way of example, in FIG. 10A shows a first stage where LDs 50 ₄, 50 ₅,50 ₆ and 50 ₇ are operated at a beginning of a scan line, while LDs 50₁, 50 ₂, and 50 ₃ that project light near or past an edge of facet 81are not used. Optionally, the system is configured for operating halfthe light sources for writing each spot and/or pixel on the exposurepanel. Referring now to FIG. 10B, as polygon 80 rotates, LDs 50 ₂, 50 ₃,50 ₄, 50 ₅ and 50 ₆ are operated and LD 50 ₁ and 50 ₇ are turned off sothat only beams that are directed toward facet 81 are operated.Referring to FIG. 10C, as polygon 80 fulther rotates, LDs 50 ₁, 50 ₂, 50₃, and 50 ₄ are operated and LD 50 ₅, 50 ₆ and 50 ₇ are turned off. InFIG. 10D, an additionally scan line is started with facet 82 by shiftingback to operating first portion of the light sources, LDs 50 ₄, 50 ₅, 50₆ and 50 ₇ In this manner facet tracking may be achieved while AOM 70 isoperated at a single RF frequency. Typically, when only a portion of thelight sources are operated at any one time, the achievable output poweris compromised. Optionally, a larger array and/or more than one arraymay be used to scale up the output power.

Reference is now made to FIG. 11 showing a simplified schematic drawingof an exemplary illumination unit including two dense arrays of lightsources and optics for combining beams from the two arrays in accordancewith some embodiments of the present invention. Typically, the number ofindividual beams that can fit through an aperture of an AOM is limited.According to some embodiments of the present invention, output power canbe further increased by combining beams from two or more light sourcesinto a single beam. According to some embodiments of the presentinvention, improved scalability of the illumination is achieved by usingan illumination unit 101 that includes more than one array, e.g. array51 and array 52 and combining beams from the different arrays.Typically, array 51 has a different corresponding wavelength and/orpolarization than array 52 so that the beams from each array can becombined with low and/or no loss of power. According to some embodimentsof the present invention, beam array 650 ₁ and 650 ₂ are combined intoone beam array 67 using a polarization splitter 94 and/or a wavelengthselective element 92. Optionally, each of arrays 51 and 52 can bereplaced with a matrix of LDs that are combined to form a single scaledmatrix of beams.

Reference is now made to FIG. 12 showing a schematic diagram of anexemplary optical design for combining beams from different arrays inaccordance with some embodiments of the present invention. According tosome embodiments of the present invention, LDs from four differentarrays are combined into a single array. According to some embodimentsof the present invention, a wavelength selective element 92 combinesbeams of different wavelengths and a polarization splitter 94 combinesbeams of different polarization. For example an LD 51 ₁ and 51 ₂ fromtwo different arrays have a same wavelength but different polarizationand a LD 51 ₁ and 52 ₁ are different in wavelength but have a samepolarization. Similarly LD 51 ₂ and 52 ₂ are different in wavelength buthave a same polarization. Optionally, beams from 51 ₁, 51 ₂, 52 ₁ and 52₂ can all be combined since each differs in at least one of wavelengthand polarization.

Reference is now made to FIG. 13 showing an exemplary DI system inaccordance with some embodiments of the present invention. According tosome embodiments of the present invention, in a DI system 100,illumination from array 50 of LDs is collimated with a collimatingoptical lens 61 and directed toward AOM 70 for modulation. The modulatedbeam provided by AOM 70 is directed toward rotating polygon 80 forscanning onto a recording medium 95 as the recording medium is scannedin a scan direction 85. Typically, illumination diverted by rotatingpolygon 80 is magnified with scanning optics 90 prior to exposingrecording medium 95. According to some embodiments of the presentinvention, the scanning rate is adjusted to equal the acoustic velocityrate of AOM 70 multiplied by the magnification provided scanning optics90 to provide for repeatedly exposing spots and/or pixels with aplurality of the LDs in array 50 using the Scophony scanning effect. Insome exemplary embodiments, the polygon is rotated at a rate of 3000RPM.

The terms “comprises”, “comprising”, “includes”, “including”, “having”and their conjugates mean “including but not limited to”.

The term “consisting of means “including and limited to.”

The term “consisting essentially of means that the composition, methodor structure may include additional ingredients, steps and/or parts, butonly if the additional ingredients, steps and/or parts do not materiallyalter the basic and novel characteristics of the claimed composition,method or structure.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable sub-combination or as suitable in any other describedembodiment of the invention. Certain features described in the contextof various embodiments are not to be considered essential features ofthose embodiments, unless the embodiment is inoperative without thoseelements.

1. A direct imaging system comprising: an illumination unit comprising aplurality of light sources, the plurality of light sources configured toemit a plurality of beams; an optical system for forming the pluralityof beams to be aligned in position or angle; an acoustic opticalmodulator positioned to receive the plurality of beams aligned in one ofposition or angle and to consecutively diffract different portions ofthe plurality of beams as an acoustic wave propagates in an acousticdirection; and a scanning element adapted to scan an exposure plane withthe plurality of beams modulated by the acoustic optical modulator at ascanning velocity, wherein the scanning velocity is selected toincoherently unite the different portions of the plurality of beams intoa single exposure spot.
 2. The system according to claim 1, wherein theplurality of light sources is plurality of semiconductor laser diodes.3. The system according claim 1, wherein at least one light source ofthe plurality of light sources is adapted to emit light at a differentwavelength than at least one other light source of the plurality oflight sources.
 4. The system according to claim 1, wherein the pluralityof light sources emits light at a range between 370-410 nm.
 5. Thesystem according to claim 1, wherein at least one light source of theplurality of light sources is adapted to have a polarization that isdifferent than at least one other at least one light source of theplurality of light sources.
 6. The system according to claim 1, whereinthe plurality of light sources is arranged in one or more arrays,wherein each array aligned with a scan direction of the direct imagingsystem.
 7. The system according to claim 6, wherein each of the arraysincludes 2-100 light sources.
 8. The system according to claim 1,wherein only a portion of the light sources are operated at a time. 9.The system according to claim 8, wherein the scanning element is arotating polygon including a plurality of facets, and wherein portion ofthe light sources that are operated are selected responsive to an angleof one of the plurality of facets during scanning.
 10. The systemaccording to claim 1, wherein each light source in the plurality oflight sources is associated with a dedicated lens, wherein the dedicatedlens is adapted to shape a beam emitted from a light source.
 11. Thesystem according to claim 10, wherein the dedicated lens is adapted toshape the beam to be elongated in a direction perpendicular to the scandirection.
 12. The system according to claim 10, wherein the dedicatedlens is adapted to shape the beam to be elongated in a directionperpendicular to the cross-scan direction.
 13. The system according toclaim 10, wherein the acoustic optical modulator is associated with anaperture for receiving the plurality of beams and wherein the dedicatedlens and the optical system is adapted to shape the beam to fill theaperture in at least one of a direction perpendicular to a scandirection and a direction perpendicular to a cross-scan direction. 14.The system according to claim 11, wherein the optical system includes anelement adapted to collimate beams from the plurality of light sourcesdirected toward the acoustic optical modulator.
 15. The system accordingto claim 11, wherein the optical system includes a telecentric opticalsystem adapted to direct the plurality of beams to an aperture of theacoustic optical modulator.
 16. The system according to claim 11,wherein each of the different portions of the plurality of beamsincludes a portion from each of the plurality of beams received from theacoustic optical modulator.
 17. The system according to claim 11,wherein each of the different portions of the plurality of beamsincludes one or more beams from the plurality of beams.
 18. The systemaccording to claim 1, wherein the scanning velocity is defined to matchan acoustic velocity of acoustic optical modulator times a magnificationratio of the system but in an opposite direction.
 19. The systemaccording to claim 1, wherein the acoustic optical modulator is amulti-channel acoustic optical modulator.
 20. The system according toclaim 1, comprising: at least two of the illumination unit; and at leastone optical element for combining corresponding beams from the at leasttwo of the illumination unit.
 21. The system according to claim 20,wherein corresponding beams from the more than one illumination unitdiffer in at least one of wavelength and polarization.
 22. A method fordirect imaging, the method comprising: providing an illumination unitincluding a plurality of light sources adapted to emit a plurality ofbeams; directing the plurality of beams toward an acoustic opticalmodulator so that the plurality of beams are aligned one of position orangle; consecutively diffracting different portions of the plurality ofbeams while an acoustic wave propagates in an acoustic direction; andscanning an exposure plane in a scan direction with output from theacoustic optical modulator, wherein the scanning is performed at ascanning velocity, and wherein the scanning velocity is selected toincoherently unite the different portions of the plurality of beams intoa single exposure spot.
 23. The method according to claim 22, whereinthe plurality of light sources includes is a plurality of semiconductorlaser diodes.
 24. The method according to claim 22, wherein at least onelight source of the plurality of light sources is adapted to emit lightat a different wavelength than at least one other light source in theplurality of light sources.
 25. The method according to claim 24,wherein the array of light sources emits light at a range between370-410 nm.
 26. The method according to claim 22, wherein at least onelight source of the plurality of light sources is adapted to have apolarization that is different than at least one other light source inthe plurality of light sources.
 27. The method according to claim 22,wherein the plurality of light sources is arranged in one or morearrays, wherein each array aligned with a direction of the scanning. 28.The method according to claim 27, wherein each of the arrays includes2-100 light sources.
 29. The method according to claim 22, comprisingoperating only a portion of the light sources at a time.
 30. The methodaccording to claim 29, wherein the portion of the light sources that areoperated are selected responsive to an angle of a facet used for thescanning.
 31. The method according to claim 22, comprising shaping eachof the plurality of beams to be elongated in a direction perpendicularto a scan direction of the scanning.
 32. The method according to claim22, comprising shaping each of the plurality of beams to be elongated ina direction perpendicular to a cross-scan direction of the scanning. 33.The method according to claim 22, comprising shaping each of theplurality of beams to fill an aperture of the acoustic optical modulatorin at least one of a direction perpendicular to a scan direction of thescanning and a direction perpendicular to a cross-scan direction of thescanning.
 34. The method according to claim 22, wherein each of thedifferent portions of the plurality of beams includes a portion fromeach of the plurality of beams received from the acoustic opticalmodulator.
 35. The method according to claim 22, wherein each of thedifferent portions of the plurality of beams includes one or more beamsfrom the plurality of beams.
 36. The method according to claim 22,comprising collimating beams from the plurality of light sourcesdirected toward the acoustic optical modulator.
 37. The method accordingto claim 22, comprising matching an acoustic velocity of acousticoptical modulator times a magnification ratio of the system but in anopposite direction.
 38. The method according to claim 22, comprising:providing a plurality of illumination units and combining correspondingbeams from the plurality of illumination units.
 39. The method accordingto claim 38, wherein the corresponding beams from the more plurality ofillumination units differ in at least one of wavelength andpolarization.
 40. A method for facet tracking in a direct imagingsystem, the method comprising: providing an array of light sourcesadapted to emit an array of beams, wherein the array of light sources isaligned with a scan direction of the direct imaging system; directingthe beams from the array of lights sources toward an acoustic opticalmodulator so that the plurality of light sources project light along alength greater than length of a single facet of a rotating polygon usedfor scanning; scanning an exposure plane in the scan direction withoutput from the acoustic optical modulator; and selectively operatingdifferent subsets of the lights sources in coordination with rotation ofthe polygon, wherein the subsets of the light sources selected are lightsources that impinge on a facet used for scanning.
 41. The methodaccording to claim 40, comprising adjusting each light source of arrayto have a different angle of incidence in acoustic optical modulator sothat the plurality of beams operated impinge along a length of the facetused for scanning.
 42. The method according to claim 40 comprisingturning off light sources from the plurality of light sources that emitbeams that impinge near or past an edge of the facet used for scanningin coordination with rotation of the polygon.
 43. The method accordingto claim 40, comprising incoherently uniting the plurality of beamsoperated into a single exposure spot.